In the design and manufacture of semiconductor devices, it has been proposed to fabricate semiconductor devices in gallium arsenide substrates. The use of gallium arsenide provides certain advantages over the more commonly used silicon substrates. For some applications, however, it has been proposed to fabricate semiconductor devices in a thin gallium arsenide layer which has been epitaxially deposited onto a silicon substrate.
A layer of gallium arsenide is typically formed on a silicon substrate by growth of the gallium arsenide layer on the silicon at temperatures of about 650.degree. C. Warpage problems, however, frequently arise with gallium arsenide layers formed by these processes. It has been suggested that these warpage problems arise from the fact that the thermal expansion coefficient of gallium arsenide is approximate twice that of silicon. Accordingly, when the combination of the newly grown gallium arsenide layer on the silicon substrate is cooled to ambient conditions, the gallium arsenide layer contracts significantly more than the silicon substrate material. This increased contraction by one layer of the composite causes the composite to warp, with the surface of the gallium arsenide layer forming a concave surface. This concave surface is disadvantageous for further semiconductor fabrication processes on the gallium arsenide layer, particularly masking and patterning operations.
It is desirable to form a gallium arsenide layer on a silicon substrate in such a manner as to reduce or eliminate the warpage of the gallium arsenide layer upon cooling of the structure to room temperature conditions.